Direct fluorination of materials with fluorine gas is a highly desirable process, but prior attempts to use direct fluorination have often produced low to mediocre yields. This is because direct fluorination reactions involving elemental fluorine are characterized by quick evolution of large quantities of heat, ignition and flaming which promote product decomposition, often with explosive violence. The inability to control direct fluorination reactions so that high yields of the desired fluorinated material could be obtained has prevented direct fluorination from becoming a widely accepted method of fluorination.
One of the more promising developments in the field of direct fluorination is a process known as the La-Mar process. In this process, the material to be fluorinated is contacted with a mixture of fluorine gas and an inert gas in which the fluorine has a very low initial concentration. The concentration of fluorine is gradually increased to maintain thermodynamic and kinetic control of the reaction until the desired degree of fluorination has been achieved. See Lagow, R. J. and Margrave, J. L., "Direct Fluorination of Organic and Inorganic Substances," Proc. Natl. Acad. Sci., 67, 4, 8A (1970).
A significant extension of the La-Mar direct fluorination process is described in U.S. Pat. No. 4,113,435 issued to Lagow et al. Therein, a cryogenic zone reactor, and method for employing such a reactor, are disclosed which permit the La-Mar process to be employed in the direct fluorination of compounds which had previously been difficult to fluorinate, such as oxygen-containing compounds including ethers, esters, ketones, alcohols, and carboxylic acids.